Pick and place tool grinding

ABSTRACT

The present invention relates to a method and system ( 100 ) for ensuring a predetermined level of accuracy of a parallel orientation of a tool tip surface ( 112 ) with respect to a work piece holder ( 110 ) surface ( 108 ) of an assembly device. A grinding plate ( 130 ) is provided onto the work piece holder surface and a grinding material is deposited thereupon. The tool tip ( 106 ) is then moved to a predetermined distance above the grinding plate and moved relative to the grinding plate in a plane oriented substantially parallel to the grinding plate top surface ( 128 ). At a plurality of predetermined locations on the tool tip surface a distance between the tool tip surface and the work piece holder surface is measured and a level of accuracy of a parallel orientation of the tool tip surface with respect to the work piece holder surface is determined in dependence upon the measured distances. Grinding the tool tip surface, measuring the distances, and determining the level of accuracy is then repeated until the level of accuracy is above a predetermined threshold.

This invention relates generally to the field of chip assembly and more particularly to a method and system for pick and place tool tip exchange.

Various packaging techniques for Integrated Circuits (ICs) have been developed to satisfy demands for miniaturization. Improved techniques for miniaturization of ICs enabling the integration of millions of circuit elements into a single IC semiconductor die have resulted in an increased demand for methods to package the semiconductor die reliably in a mass-production.

Flip chip assembly is a mounting method used for mounting a semiconductor die to an external circuitry such as a circuit board that obviates employment of connecting wires. Instead, a solder ball is deposited onto each semiconductor die contact pad, which is then directly connected to a respective contact of the external circuitry.

For mounting the semiconductor die to the external circuitry a pick and place tool is used. The pick and place tool picks the semiconductor die with its tip at a predetermined location—using, for example, gripping jaws or suction—and places it onto a respective location on an external circuitry which is hold at a predetermined location on a work piece holder such that the solder balls are facing the external circuitry. The solder balls are then molten to produce an electrical connection with respective contacts of the external circuitry using, for example, ultrasonic heating.

With increasing miniaturization the flip chip assembly needs to provide improved quality of contact between the semiconductor die contact pads and the respective contacts of the external circuitry. In order to ensure a same quality of contact for all contact pads of the semiconductor die it is necessary to provide a highly accurate parallel orientation of the semiconductor die with respect to the external circuitry—i.e. between a plane tool tip surface accommodating a surface of the semiconductor die opposite the solder balls and a plane work piece holder surface accommodating the external circuitry.

In order to provide flexibility in a mass production assembly line, state of the art pick and place assembly equipment is typically provided with interchangeable tool tips in order to accommodate different sized semiconductor dies.

Unfortunately, the provision of interchangeable tool tips substantially reduces the accuracy of the parallel orientation between the tool tip surface and the work piece holder surface, i.e. it is not possible to reliably mount the interchangeable tool tips at a high level of accuracy of the parallelism, thus, impeding use of pick and place tools having interchangeable tool tips in the mass production of highly miniaturized ICs.

It would be highly desirable to overcome these drawbacks and to provide a method and system for pick and place tool tip exchange with a grinding process for ensuring a predetermined level of accuracy of the parallel orientation.

In accordance with the present invention there is provided a method for ensuring a predetermined level of accuracy of a parallel orientation of a tool tip surface with respect to a work piece holder surface of an assembly device. The method is implemented in an assembly device comprising a work piece holder having a substantially plane work piece holder surface. The work piece holder surface is used for accommodating a first component thereupon. The assembly device further comprises a tool tip having a substantially plane tool tip surface for accommodating a second component thereupon. The tool tip is used for placing the second component at a predetermined location onto the first component. A grinding plate is provided onto the work piece holder surface and a grinding material is deposited thereupon. The tool tip is then moved to a predetermined distance above the grinding plate top surface. The tool tip surface is then moved relative to the grinding plate top surface in a plane oriented substantially parallel to the grinding plate top surface. Through abrasive action of the grinding particles, material is removed from the tool tip surface such that the tool tip surface is oriented parallel to the work piece holder surface 108 at an increased level of accuracy. At a plurality of predetermined locations on the tool tip surface a distance between the tool tip surface and the work piece holder surface is measured and a level of accuracy of a parallel orientation of the tool tip surface with respect to the work piece holder surface is determined in dependence upon the measured distances. Grinding the tool tip surface, measuring the distances, and determining the level of accuracy is then repeated until the level of accuracy is above a predetermined threshold.

In accordance with the present invention there is provided a system for ensuring a predetermined level of accuracy of a parallel orientation of a tool tip surface with respect to a work piece holder surface of an assembly device. The system is implemented in an assembly device comprising a work piece holder having a substantially plane work piece holder surface. The work piece holder surface is used for accommodating a first component thereupon. The assembly device further comprises a tool tip having a substantially plane tool tip surface for accommodating a second component thereupon. The tool tip is used for placing the second component at a predetermined location onto the first component. The system comprises an output port for being connected to a control mechanism of the assembly device. The system further comprises an input port for being connected to a height measurement device for receiving a signal in dependence upon measurements at a plurality of predetermined locations on the tool tip surface of a distance between the tool tip surface and the work piece holder surface. Electronic circuitry is connected to the input port and the output port. The electronic circuitry is used to: determine a level of accuracy of a parallel orientation of the tool tip surface with respect work piece holder surface in dependence upon the measured distances; determine a particle size of the grinding material in dependence upon the measured distances; determine a grinding distance between the tool tip surface and the work piece holder surface in dependence upon the measured distances and generating a grinding distance control signal in dependence thereupon; generate a grinding movement control signal indicative of a relative movement between the tool tip and the work piece holder; and, provide the grinding distance control signal and the grinding movement control signal to the output port.

In accordance with the present invention there is further provided a storage medium having stored therein executable commands for execution on a processor. The processor when executing the commands performs a method for ensuring a predetermined level of accuracy of a parallel orientation of a tool tip surface with respect to a work piece holder surface of an assembly device. The method is implemented in an assembly device comprising a work piece holder having a substantially plane work piece holder surface. The work piece holder surface is used for accommodating a first component thereupon. The assembly device further comprises a tool tip having a substantially plane tool tip surface for accommodating a second component thereupon. The tool tip is used for placing the second component at a predetermined location onto the first component. The processor receives a measurement signal from a height measurement device mounted to the assembly device. The measurement signal is indicative of measurements at a plurality of predetermined locations on the tool tip surface of a distance between the tool tip surface and the work piece holder surface. The processor then determines a level of accuracy of a parallel orientation of the tool tip surface with respect to the work piece holder surface in dependence upon the measured distances and a particle size of the grinding material in dependence upon the measured distances.

Exemplary embodiments of the invention will now be described in conjunction with the following drawings, in which:

FIG. 1 is a simplified block diagram illustrating a pick and place assembly device system according to the invention;

FIG. 2 is a simplified flow diagram illustrating a method for ensuring a predetermined level of accuracy of the parallel orientation according to the invention; and,

FIGS. 3 a and 3 b are a simplified block diagrams illustrating in cross-sectional views a tool tip placed above a grinding plate with grinding material placed therebetween in the method according to the invention described in FIG. 2.

The following description is presented to enable a person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the embodiments disclosed, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

While the invention will be described in combination with a pick and place equipment for flip chip assembly, it will become apparent to those skilled in the art that the invention is not limited thereto but is also applicable for various other pick and place assembly equipment as well as other assembly equipment where accurate parallel orientation of two facing work surfaces with respect to each other is of importance.

Referring to FIG. 1, a pick and place assembly device system 100 according to the invention is shown. The pick and place assembly device system 100 comprises a base 102 having a head assembly 104 movable mounted thereto. The head assembly accommodates an interchangeable tool tip 106 movable with respect to three space coordinates x, y, and z, with the coordinates x and y being oriented parallel to a work piece holder surface 108 of work piece holder 110 mounted to the base 102, and the coordinate z being oriented perpendicular thereto. The work piece holder 110 accommodates a first component such as, for example, an external circuitry upon its substantially plane work piece holder surface 108 using, for example, a clamping mechanism. The tool tip 106 accommodates a second component such as, for example, a semiconductor die upon its substantially plane tool tip surface 112 using, for example, a clamping mechanism or suction. The tool tip 106 is then moved for placing the second component at a predetermined location onto the first component. With increasing miniaturization it is necessary to provide a highly accurate parallel orientation of the semiconductor die with respect to the external circuitry, i.e. the tool tip surface 112 and the work piece holder surface 108, respectively.

Referring to FIG. 2, a simplified flow diagram of a method for ensuring a predetermined level of accuracy of the parallel orientation according to the invention is shown. The method is implemented, for example, after mounting the tool tip 106 to the head assembly 104 and performing adjustments according to manufacturer specifications of the pick and place assembly device. Optionally, the method is also implemented during mass assembly, for example, in predetermined time intervals in order to ensure accurate parallel orientation.

At 10, a plurality of locations on the tool tip surface 112 are determined for determining the parallel orientation using, for example, a processor 114 of grinding control system 116. For example, the locations are determined in dependence upon a size of a contact surface of the second component and in dependence upon a predetermined threshold for the accuracy. As is well known, a plane is, for example, defined in space by the coordinates of three points, therefore, it is possible to determine the orientation of the tool tip surface based on three measurements. However, in order to increase accuracy the number of locations is increased. For example, the locations are determined in x and y coordinates for various sizes and levels of accuracy during an empirical test phase and stored in the form of a look up table in memory 118 of the grinding control system 116. Using height measurement device 120 connected to measurement control port 122 a vertical distance between the tool tip surface 112 and the work piece holder surface 108 is measured at the predetermined locations—at 12.

For example, the processor 114 provides control signals indicative of the x and y coordinate of each location and in response thereupon the height measurement device 120 performs the measurement at the respective location and provides a signal indicative of a distance to the processor 114. The height measurement device 120 comprises, for example, a mechanical touch sensor having a needle 124 that is movable between contact with the tool tip surface 112 and the work piece holder surface 108. At times other than measurement times the height measurement device 120 is retracted and, optionally, covered for protection. Alternatively, an optical measurement device is employed. Using the processor 114, a level of accuracy of a parallel orientation of the tool tip surface 112 with respect to the work piece holder surface 108 is then determined in dependence upon the measured distances—at 14.

If the level of accuracy is above the predetermined threshold, a signal indicative thereof is, for example, displayed on display 126 of the grinding control system 116. If the level of accuracy is below the predetermined threshold, a particle size of grinding material is determined in dependence upon the measured distances, for example, based on a difference between the distances—at 16. For example, in case of a larger difference between the distances a larger amount of material is to be removed from the tool tip surface 112 using larger sized grinding material particles. At 18, a grinding distance between the tool tip surface 112 and a grinding plate top surface 128 of grinding plate 130 is determined in dependence upon the measured distances or the grinding material particle size. For example, for larger grinding particles a larger grinding distance is used. At 20, a grinding time interval is determined in dependence upon the measured distances and, optionally, the grinding material particle size. For example, grinding material particle sizes, grinding distances, and grinding time intervals have been determined for various parameter combinations during an empirical test phase and stored in the form of a look up table in the memory 118 of the grinding control system 116.

At 22, the grinding plate 130 is provided onto the work piece holder surface 108 and hold in place using, for example, the clamping mechanism used for holding the first component, followed by depositing the grinding material having the predetermined particle size onto the top surface 128 of the grinding plate 130—at 24. For example, the tool tip 112 is made of tungsten carbide (WCr) with a hardness of approximately 9 Mohs. The grinding plate 130 is made of a material having a hardness greater equal to the hardness of the tool tip 112 such as, for example, aluminum oxide (Al₂O₃). As grinding material an abrasive paste comprising particles having a hardness greater than the tool tip 112 and the grinding plate 130 is used such as, for example, a diamond paste—having a particle hardness of 10 Mohs. Depending an the measured distances the particle size chosen is, for example, 45 μm, 25 μm, 10 μm, 3 μm, or smaller. As is evident, while described for grinding of a very hard material, this process is also possible to implement for grinding various other materials such as various types of steel or plastic materials with proper adaptation of the grinding material.

At 26, the tool tip surface 112 is then moved to the predetermined grinding distance D above the grinding plate top surface 128, using the head assembly 104 controlled by the processor 114 via control port 132, as illustrated in FIG. 3 a. Grinding is then performed —at 28—by providing relative movement between the tool tip surface 112 and the grinding plate top surface 128 in the x, y plane, as shown in FIG. 3 b, for the duration of the grinding time interval. Through abrasive action of the grinding particles 133, material is removed from the tool tip surface 112 such that the tool tip surface 112 is oriented parallel to the work piece holder surface 108 at an increased level of accuracy. For example, the tool tip surface 112 is moved linearly in various directions or in a circular fashion. After elapse of the grinding time interval the grinding process is stopped, the grinding plate 130 removed, and the measurement 12 repeated. Depending on the level of accuracy the following steps 14 to 28 are then repeated using, for example, smaller sized grinding particles, until the level of accuracy is greater equal to the predetermined threshold.

As is evident, it is possible to implement the method for ensuring a predetermined level of accuracy according to the invention in an automated fashion using the system 116 described in FIG. 1. For example, after mounting of the tool tip 106 and adjustments according to the manufacturers specifications a user is able to provide, via a user interface 143 such as a keyboard or touch-screen, control commands indicative of, for example, size of the second component and predetermined threshold for the level of accuracy. The system 116 then performs the steps 10 to 20 in an automated fashion and provides information to the user regarding particle size of the grinding material using, for example, the display 126. The user then provides the grinding plate 130 and the grinding material 133, followed by steps 26 and 28 performed again in an automated fashion with the system 116 controlling the head assembly 104. Optionally, a mechanism for providing and removing the grinding plate 130 and depositing the respective grinding material is provided controlled by the system 116.

The system 116 is implemented using, for example, a workstation comprising the processor 114 for executing executable commands stored in the memory 118 for performing the processing steps described above. Alternatively, at least a portion of the processing steps are performed in a hardware implemented fashion. As is evident, it is possible to provide the system 116 and the height measurement device 120 as a retrofit for installation in existing assembly equipment. Furthermore, some existing assembly equipment comprises a height measurement device such as an integrated tough down sensor, which is possible to employ for the distance measurements controlled by the system 116.

Numerous other embodiments of the invention will be apparent to persons skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims. 

1. A method comprising: providing an assembly device comprising: a work piece holder having a substantially plane work piece holder surface, the work piece holder surface for accommodating a first component thereupon; a tool tip having a substantially plane tool tip surface for accommodating a second component thereupon, the tool tip for placing the same at a predetermined location onto the first component; providing a grinding plate onto the work piece holder surface; depositing grinding material onto a top surface of the grinding plate; moving the tool tip to a predetermined distance above the grinding plate top surface; and, grinding the tool tip surface by providing relative movement between the tool tip surface and the grinding plate top surface in a plane oriented substantially parallel to the grinding plate top surface.
 2. A method as defined in claim 1 comprising: measuring at a plurality of predetermined locations on the tool tip surface a distance between the tool tip surface and the work piece holder surface; and, determining a level of accuracy of a parallel orientation of the tool tip surface with respect to the work piece holder surface in dependence upon the measured distances.
 3. A method as defined in claim 2 comprising: repeating grinding the tool tip surface, measuring the distances, and determining the level of accuracy until the level of accuracy is above a predetermined threshold.
 4. A method as defined in claim 3 comprising determining a particle size of the grinding material in dependence upon the measured distances.
 5. A method as defined in claim 4 comprising determining the predetermined distance of the tool tip surface above the grinding plate top surface in dependence upon the measured distances.
 6. A method as defined in claim 4 comprising depositing grinding material having a second particle size.
 7. A method as defined in claim 3 wherein measuring the distances, and determining the level of accuracy is performed at a predetermined time instance.
 8. A method as defined in claim 7 wherein the time instance is determined in dependence upon the measured distances.
 9. A method as defined in claim 2 wherein the predetermined locations are determined in dependence upon a size of a contact surface of the second component.
 10. A method as defined in claim 9 wherein the predetermined locations are determined in dependence upon the predetermined threshold.
 11. A method as defined in claim 2 wherein at least three predetermined locations are determined.
 12. A method as defined in claim 1 wherein a pick and place assembly device is provided.
 13. A method as defined in claim 12 wherein a pick and place assembly device for flip chip assembly is provided.
 14. A system comprising: an output port for being connected to a control mechanism of an assembly device, the assembly device comprising: a work piece holder having a substantially plane work piece holder surface, the work piece holder surface for accommodating a first component thereupon; a tool tip having a substantially plane tool tip surface for accommodating a second component thereupon, the tool tip for placing the same at a predetermined location onto the first component; an input port for being connected to a height measurement device for receiving a signal in dependence upon measurements at a plurality of predetermined locations on the tool tip surface of a distance between the tool tip surface and the work piece holder surface; and, electronic circuitry connected to the input port and the output port for: determining a level of accuracy of a parallel orientation of the tool tip surface with respect to the work piece holder surface in dependence upon the measured distances; determining a particle size of the grinding material in dependence upon the measured distances; determining a grinding distance between the tool tip surface and the work piece holder surface in dependence upon the measured distances and generating a grinding distance control signal in dependence thereupon; generating a grinding movement control signal indicative of a relative movement between the tool tip and the work piece holder; and, providing the grinding distance control signal and the grinding movement control signal to the output port.
 15. A system as defined in claim comprising a user interface connected to the electronic circuitry receiving user input commands and for displaying data in dependence upon at least one of the level of accuracy, the particle size, the grinding distance, and the grinding movement.
 16. A system as defined in claim 15 comprising memory connected to the electronic circuitry, the memory having stored therein executable commands for execution on the electronic circuitry.
 17. A system as defined in claim 15 comprising a second output port connected to the electronic circuitry, the second output port for being connected to the height measurement device, the electronic circuitry for determining the predetermined locations and for providing a height measurement control signal in dependence thereupon to the second output port.
 18. A storage medium having stored therein executable commands for execution on a processor of a grinding control system, the processor when executing the commands performing: receiving a measurement signal from a height measurement device mounted to an assembly device, the assembly device comprising: a work piece holder having a substantially plane work piece holder surface, the work piece holder surface for accommodating a first component thereupon; a tool tip having a substantially plane tool tip surface for accommodating a second component thereupon, the tool tip for placing the same at a predetermined location onto the first component; the measurement signal being indicative of measurements at a plurality of predetermined locations on the tool tip surface of a distance between the tool tip surface and the work piece holder surface; determining a level of accuracy of a parallel orientation of the tool tip surface with respect to the work piece holder surface in dependence upon the measured distances; and, determining a particle size of the grinding material in dependence upon the measured distances.
 19. A storage medium as defined in claim 18 having stored therein executable commands for execution on a processor of a grinding control system, the processor when executing the commands performing determining a grinding distance between the tool tip surface and the work piece holder surface in dependence upon the measured distances.
 20. A storage medium as defined in claim 19 having stored therein executable commands for execution on a processor of a grinding control system, the processor when executing the commands performing determining a grinding time interval in dependence upon the measured distances.
 21. A storage medium as defined in claim 19 having stored therein executable commands for execution on a processor of a grinding control system, the processor when executing the commands performing determining the predetermined locations in dependence upon a size of a contact surface of the second component.
 22. A storage medium as defined in claim 21 having stored therein executable commands for execution on a processor of a grinding control system, the processor when executing the commands performing determining the predetermined locations in dependence upon the predetermined threshold. 